SK282036B6 - Method and device for disposing of a solution containing an organic acid, device for performing of this method - Google Patents

Abstract

The method is intended for the disposal of an aqueous solution which contains an organic acid and an iron complex and is generated as waste, in particular during the decontamination of radioactively contaminated surfaces of building components. The iron complex is reduced in solution by irradiation with ultraviolet radiation. A dissolved iron salt is formed and carbon dioxide is removed and removed. An oxidizing agent is then added to the solution, which contains the dissolved iron salt and the organic acid. In the process, water is formed and the iron complex is formed again. A portion of the dissolved iron salt is removed from the solution using a cation exchange resin. The solution containing the iron complex is irradiated again with ultraviolet radiation. A cycle is formed which lasts until all of the organic acid has been consumed. An apparatus for carrying out this method is also described

Description

Technical field

The present invention relates to a process for the disposal of an aqueous solution containing an organic acid and an iron complex and which is produced as waste, in particular in the decontamination of radioactive contaminated surfaces of building components. The invention also relates to an apparatus for carrying out this method with a solution tank comprising an organic acid and an iron complex.

BACKGROUND OF THE INVENTION

A method and an apparatus for the disposal of an organic substance are known from DE-A-41 26 971. By means of this method and the corresponding apparatus, the organic acids used for decontamination of the surface of radioactive contaminated components are treated.

After such decontamination, there remains a solution which, in addition to the proportion of acids which has not been chemically altered, contains chemicals formed during decontamination as well as radioactive substances which have been removed from the surface of the components. Such a solution must be solidified and finally stored in drums.

In order to accommodate as little final storage as possible, there is an attempt to reduce the volume of the solution before hardening.

It is known that hydrogen peroxide is introduced into the solution while in contact with the catalyst. Carbon dioxide and video are then formed as essential decomposition products. The concentration of the solution is thereby reduced, so that after one evaporation stage only a relatively small volume remains, which must be solidified and fed to the final depot.

The known method and the corresponding apparatus need a catalyst for the disposal of the organic substance. Such a catalyst must be brought into contact with the substance. Thereafter, the fixed catalyst substance must be kept floating in the liquidated solution. A variant requires costly maintenance of the catalyst.

During decontamination, metals in the form of anions and cations are produced as waste. Usually anion exchangers and cation exchangers are used to remove these metal ions. The anion exchanger removes the anionic metal complexes and also the decontamination chemicals. Then a big anion exchanger is needed. This results in a large amount of ion exchange resin which must be removed.

As a rule, the remaining solution is evaporated and the concentrate thus obtained is finally stored. Finally, the decontaminated system is rinsed and the rinsing water is evaporated. Thus, very large amounts of solutions or water must be treated.

The object of the invention was to provide a process for the disposal of an aqueous solution containing an organic acid which does not require the use of a costly catalyst. Appropriate equipment for the disposal of such an aqueous solution should also be provided.

In particular, after decontamination, little ion-exchange resin is to be produced as waste, and large amounts of solution that do not have to be disposed of are to be produced.

SUMMARY OF THE INVENTION

The first object is achieved according to the invention by irradiating the solution with ultraviolet radiation, thereby reducing the iron complex and forming a dissolved iron salt and carbon dioxide, removing part of the dissolved iron salt from the solution by cation exchange, removing the other part of the dissolved salt the iron, the acid portion and the added oxidant form water and re-form the iron complex, and that the remaining solution containing the iron complex and still unassociated organic acid is irradiated again by ultraviolet radiation and the cycle is continued until the organic acid is completely removed.

The iron complex present in the aqueous solution to be disposed of has entered this solution, for example, during decontamination. Such a solution may also contain chromium-nickel complexes which, instead of the iron complex, may contribute to the disposal of the aqueous solution containing the organic acid.

The process according to the invention achieves the advantage that the organic acid present in the solution is completely converted to carbon dioxide and water without the need for a catalyst. The process for the disposal of the organic acid can already be started during decontamination. No expensive equipment is required. The process can be carried out, for example, directly in a tank which is decontaminated. Carbon dioxide can be removed as it does not contain radioactive substances.

The re-formed iron complex is advantageously reused in the process of the invention. This creates a circular storyline.

The cycle determines that complex iron anions are preferably converted to iron cations. Therefore, only cation exchangers must be used, and no anion exchange resin need be used.

The amount of ion exchange resin to be removed is preferably oriented only to the actual removal of the cations of the decontaminated system. This amount of resin is about a factor of 20 less than the amount of resin produced as waste in known decontamination processes. This applies when the method of the invention is used to dispose of a saturated decontamination solution. A small amount of resin requires only a small final storage.

By means of the process according to the invention, the solution can advantageously be cleaned to such an extent that it can be reused for later operation of the decontaminated system, for example as a cooling medium.

The costly disposal of the solution with the degree of evaporation falls out. The decontaminated system does not even need to be rinsed, leaving large amounts of water as waste, which should later evaporate.

As a rule, the destroyed solution already contains an iron complex. This is formed from a portion of the removed organic acid and iron ions which are still present in the removed solution. These iron ions may reach the tank to be decontaminated, for example during the contamination process or previously.

However, if no iron ions are present in the solution, for example, ionized iron (iron ions) may be admixed to the solution to convert some of the acid into an iron complex. Thereafter, for example, an iron salt can be introduced into the solution, which ionizes there, thereby forming, among other things, iron ions. The addition of iron ions achieves the advantage that even when iron ions are to be absent in solution, iron ions are sufficiently provided to convert part of the acid into an iron complex.

Ionized iron, for example, has a certain patency and forms an iron complex with part of the acid in which the iron has the same valence (an iron complex with the same valence).

For example, the ionized iron is trivalent, forming a complex with a portion of the organic ferric acid.

By irradiation with ultraviolet radiation, this complex is converted to form a soluble iron salt in the formation of carbon dioxide, in which the iron valence is, for example, 1 smaller than the iron valence in the complex. (Iron salt, whose valency is 1 less than that of the iron complex). This dissolved iron salt, acid residue and oxidizer,

The added iron is again formed by the iron complex. In addition, water is produced.

The ferric complex is converted, for example, to a dissolved ferrous salt (ferric iron salt). This dissolved ferrous salt, the organic acid residue and the oxidizing agent that is added react chemically to form water and again the ferric complex. This ferric complex corresponds to the previous ferric complex. Thus, the ferric complex is regenerated.

In the event that the entire organic acid residue has not reacted chemically with the iron salt and oxidant because, for example, the amount of iron salt was not sufficient, the regenerated iron complex can be re-formed by irradiation with ultraviolet radiation to produce carbon dioxide and dissolved iron salt. The iron salt is then reacted with the added oxidant and the remaining organic acid to re-form the iron-water complex. Preferably, a cycle occurs until the entire amount of organic acid is converted to a relatively small amount of iron salt, which is removed by cation exchange, and to carbon dioxide and water. The carbon dioxide and water are removed.

The corresponding cycle is also possible using another ionized metal.

For example, if the organic acid is oxalic acid, reactions occur according to the following chemical equations:

(1) 3H ₂ C ₂ O ₄ + Fe ¹¹¹ -> [Fe ^m (C ₂ O ₄ ) ₃ ] ³ 'oxalic acid + iron (III) -> ferric complex (2) [Fe ^ra (C2O4) 3] ³ · + UV Fe '(C2O ₄ ) ₂ + 2 CO ₂ ferric complex + UV -> ferrous salt + CO ₂ (3) Fe (C ₂ O ₄ ) ₂ + H ₂ C ₂ O ₄ + H ₂ O ₂ ferrous salt + acid oxalic + hydrogen peroxide -> [Fe ^n, (C2O4) 3] ³ - + 2H2O -> ferric complex + H ₂ O

The ferric complex formed by the reaction of chemical equation (3) is reused in the reaction of chemical equation (2). The two chemical reactions (2) and (3) alternate until the entire amount of oxalic acid is consumed. In addition to CO ₂ and H ₂ O, only a small amount of ferrous salt remains.

An appropriate cycle is also possible with any other metal complex that may be formed initially by the ionized metal.

No separate tank is required to run the cycle. It can even take place in a previously decontaminated tank.

The organic acid, which is not converted to the ferrous salt, is converted into water and carbon dioxide, preferably without any expensive removal, by means of a cycle.

Carbon dioxide may be removed.

The oxidant may be, for example, hydrogen peroxide or ozone, which are particularly suitable.

The concentration of the oxidant is, for example, 0.002 mol / dm ³ to 0.02 mol / dm ³ , in particular 0.005 mol / dm ³ to 0.007 mol / dm ³ . At a much higher concentration of hydrogen peroxide, less organic acid would be converted due to UV-absorption of hydrogen peroxide.

A particularly suitable wavelength of the ultraviolet radiation used lies between 250 nm and 350 nm.

The second object of the invention is to provide a suitable device for disposing of an aqueous solution with a solution tank containing organic acid and an iron complex and which is produced as waste, particularly in the decontamination of radioactive contaminated building surfaces. a circulating line, that the circulating line comprises a UV-irradiation portion, and that an oxidant supply line comprising a metering device and a cation exchanger is associated with the circulation line.

In the UV-irradiation section, the iron complex present in the solution is caused to be reduced so as to form a dissolved iron salt and carbon dioxide. Carbon dioxide is removed as a gas through the outlet. An appropriate amount of oxidant is then fed via the metering device through the supply line. The supply line can be connected via a tank or directly to the UV-irradiation section or else it can flow into the circulation line. This ensures that the oxidant reaches where there is a solution at this point that contains the dissolved iron salt and the organic acid.

After the oxidant has been filled, the iron complex is formed in addition to water. This iron complex corresponds to an iron complex that had previously occurred. This ensures that a cyclic process can take place. Again, the iron complex is irradiated with ultraviolet radiation and thereby reduced. In turn, the dissolved iron salt and carbon dioxide are formed and the iron salt together with the remaining acid and oxidant re-form the iron complex as well as the water. This ring action can be continued until all the acid is consumed.

A solution inlet pipe containing iron ions may be connected to the tank or circulation pipe via a metering device. At the beginning of the process, a solution containing iron ions is filled through this inlet line if there are no iron ions in the solution present in the tank. However, iron ions are mostly found. In the absence of iron ions, no iron complex formed from the iron ions and the part of the acid to be removed could be present.

Since preferably no interfering anions are present, the remaining solution can be purified by means of a cation exchanger to such an extent that it can be reused, for example, as a cooling medium. Therefore, no evaporators are required and therefore no evaporation residues need to be removed.

The chemical cyclic process is carried out in the circulation apparatus until the partial amount of organic acid which eventually remains after the reaction has been converted. This is possible because the iron complex is not retained in the cation exchanger. When the entire amount of acid is consumed, no iron complex is formed. Eventually a small amount of iron salt remains in the solution. However, the cationic portion of this iron salt is removed from the solution by cation exchange. Likewise, radioactive cations which may be in solution from the decontamination process are removed by means of a cation exchanger. The remaining solution no longer has to be further processed and can be immediately reused as a cooling medium.

By means of the process and the control according to the invention, it is particularly advantageous that in the chemical cycle the organic acid can be completely converted into carbon dioxide and water without the use of expensive catalyst technology. In addition, after the decontamination has been carried out, neither an anion exchanger nor an evaporator are required to remove residuals.

An apparatus for disposing of an aqueous solution containing an organic acid is explained in more detail on the basis of the drawing.

DETAILED DESCRIPTION OF THE INVENTION

The drawing shows a tank 1, which may be a decontaminated tank, which is part of the circulation pipe 2. After the decontamination has been carried out, the organic acid remains in the tank 1 and must be removed. However, the tank 1 may also be a separate tank into which an aqueous disposal solution containing organic acid is filled. The tank 1 has a filling opening 11 through which the discharged solution is then filled. In the case where the decontamination is carried out in the tank 1, the decontamination chemicals are introduced into the tank 1 before the decontamination. In the event that the solution to be disposed of contains no iron complex, a supply line 3 for iron ions is proposed which can be supplied in the form of dissolved iron salt. This supply line 3 comprises a metering device 4 and flows into the circulation line 2. It can also flow directly into the tank 1. By means of iron ions, the part of the organic acid present in the solution is converted into an iron complex.

A UV-irradiation section 5 is connected to the outlet 9 of the tank 1, which is part of the circulation pipe 2. By means of irradiation with ultraviolet radiation, the iron complex in solution is reduced there, so that a dissolved iron salt and carbon dioxide are formed. The carbon dioxide exits the UV-irradiation portion 5 through the outlet 6 which is connected to it. Carbon dioxide can be evacuated as it does not contain any contaminants.

The oxidizer inlet line 7 then enters the oxidizer into the circulation line 2, at which point the iron salt dissolved and the balance of the organic acid are present. The addition of the oxidant takes place via the metering device 8 located in the supply line 7. The supply lines 3 and / or 7 may also exit at an unknown location downstream of the UV-irradiation section 5 or directly into the UV-irradiation section 5. From the dissolved salt iron, acid and oxidant portions form water, and again an iron complex that corresponds to the aforementioned iron complex. From this point on, the cycle may be repeated: The iron complex is again reduced by ultraviolet radiation to form a dissolved iron salt and carbon dioxide. The oxidant is then reacted again to form the iron-water complex from it, the iron salt and the other part of the acid. Finally, after several such cycles, the entire amount of acid is converted to carbon dioxide, water and a small amount of iron salt.

If the solution to be disposed of was a decontamination solution, the remaining solution still contains radioactive substances removed by decontamination. These substances and the cationic portion of the iron salt are removed from the solution by means of a cation exchanger 10, which may additionally be attached to the UV irradiation portion 5. No anion exchange resin is required. Nevertheless, the remaining liquid is so pure that it can be reused as a cooling medium, for example in a power plant. The cation exchanger 10 is arranged in the circulation pipe 2. It can be bridged by bypass 12 so that part of the solution can be passed around the cation exchanger 10 and thus not be released from the iron salt while iron salt is still required to re-form the iron complex. Typically, however, only one portion of the iron salt is removed by cation exchange 10 from the solution at one flow.

No evaporator is necessary to remove residual liquid. Little ion-exchange resin is produced as waste and there are no evaporation residues which would have to be removed.

The emptying opening 13 serves for emptying the illustrated device. A pump 14 may be provided in the circulation pipe 2.

Claims (9)

PATENT CLAIMS A process for the disposal of an aqueous solution comprising an organic acid and an iron complex, and is produced in particular as waste in the decontamination of radioactive contaminated building surfaces, characterized in that the solution is irradiated with ultraviolet radiation, thereby reducing the iron complex and forming dissolved iron salt. and carbon dioxide, that a portion of the dissolved iron salt is removed from the solution by means of a cation exchanger, that a second portion of the dissolved iron salt, a portion of the acid, and the added oxidant form water and iron complex again and that the remaining solution containing the iron complex and still unassociated organic acid it is irradiated with ultraviolet radiation and the cycle is continued until the organic acid is completely removed. Method according to claim 1, characterized in that ionized iron is admixed with the solution to convert part of the acid into an iron complex. Method according to claim 2, characterized in that part of the acid is converted to an iron (III) complex by means of ionized trivalent iron. Method according to one of Claims 1 to 3, characterized in that the oxidant is hydrogen peroxide or ozone. Method according to one of claims 1 to 4, characterized in that the concentration of the oxidant is 0.002 mol / dm ³ to 0.02 mol / dm ³ . The method of claim 5, wherein the oxidant concentration is 0.005 mol / dm ³ to 0.007 mol / dm ³ . Method according to one of Claims 1 to 6, characterized in that the ultraviolet radiation has a wavelength of 250 nm to 350 nm. Apparatus for carrying out the method according to one of claims 1 to 7 with a solution vessel (1) comprising an organic acid and an iron complex, characterized in that a circulation pipe (2) emerges from and flows into the tank (1). ), that the circulation line (2) comprises an ultraviolet irradiation component (5) and that the circulation line (2) is associated with an oxidant supply line (7) comprising a metering device (8) and a cation exchanger (10). Apparatus according to claim 8, characterized in that a feed line (3) for the solution containing iron ions is associated with the circulation line (2), which comprises a metering device (4).